Arcol.hu hotend v4 adaptation for Rapman machines

Preamble

As you may be aware, back in 2010, the v3 version of the hotend (the PEEK based, so not the v4 all metal one),
was compatible mechanically and electrically with Rapman machines:

Starting from v4, the thermistor was intially switched to 104-GT2, which discontinued mechanical compatibility with the Rapman:

I then migrated to a Honeywell thermistor, which enabled me to leave out the fire cement, shown here:

These changes to the v4 hotend made it technically superior to the old one, and also way faster to assemble. However, it was neither mechanically nor electrically compatible with Rapman machines.

Recently, I have been approached by two people to get manufactured a fully compatible hotend for the Rapman. Two people are almost a crowd!

So with that in mind, I think I came up with a pretty good solution:

In detail

The length of the original v4 hotend was short by design,
however to maintain mechanical compatibility with the Rapman,
it needed a longer (73mm tall) hotend.
Pictured here is the assembled unit complete with nozzle, barrel and heatsink:

The new heatsink consists of two parts:
- The heatsink itself, which is 15.5mm longer than the standard one
- a disk, which goes on top of it, what you can mount on the Rapman machine using two M5 bolts.

The lower part of the hotend needs no modification, except it is
reverted back to the firecement version for using the 204-GT thermistor.

Summarizing the modification is basically a reworked heatsink and mounting plate.

I do hope it will serve well all the rapman users, who are still out there.

I have RP parts available in three different colors: white, green and black.
Here is a comparison between green and white print:

Gears

Here is the gears I use:

You may be wondering why I am not using herringbone gears.
Herringbone gears run a little quiter, and have a tiny bit less backlash.
Also they can handle higher torque.

However it does not affect print quality.
The filament has a backlash due to its inertia, and we compensate
for backlash anyway. It has the same number of teeth, so no additional
resolution either (not that we need it).

But the main reason is that it is more troublesome to print out, for no real
advantage, so I kept the traditional spur gears. You can print a
herringbone if you wish as an upgrade.

Wade pusher (extruder upper body)

Here we go:

It is a modified Accessible Wade extruder, mainly the holes were adjusted.
It is more accurate and compatible withv4 hotend.

You can see the setup is standing on two M8 nuts, so the
hotend is lower by just enough distance then the two fans.
It is optimised for the minimum height, so you have themaximum printing height possible*.

Here are some more pictures, it is kind of rotating:)

History

You could have build this extruder setup from about february of this year (2012).
If someone would have published this extruder setup back in time, it
would have saved me some unnecessary circles.
So I hope you (dear Reader) find this article equally useful,
what I would have found it, if it was existed back then.

Printing quality

If you want to check what is possible
with our v4
hotend in regard of printing quality, or you want a trouble free
extruder setup, then go get one!

As a remainder, here it is the wade pusher printed in white:
(the white is the easiest to photograph, every irregularities are shown)

Im fairly happy with the overall printing quality, you can see it as
our current state of the art at 0.3mm layer height.

No worries, even finer layer height is possible, so it is not the
limit of what v4 is capable of.

I think Im able to print one full set per week, and for start I have
3 full sets. I know it is limited, but it is not intended for general
public, just for the quality enthusiastic and those who want
a working printer first and a DIY machine second.

I have some leftover pictures, which would be too bad to miss out:)

And even moar:

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I change slightly the commenting policy. I will close the commenting after a week of the date of publishing to prevent spams leaking through.

Why do you need a fan?

As many of you may know, I have been using a double carriage fan (modified thing:9869) for my printer.

If only the hotend needed the air movement,
a single carriage fan would suffice, yet I get better results with double carriage fan.

So first and foremost the print itself needs the fan.

Buying fans for the carriage

Choosing the right fan is not easy. The ideal fan must be able to be driven directly from a PWM output of the RAMPS.

Many fans are not capable of be driven from a PWM output,
so it's mostly a hit and miss when buying small fans.

Why is a MagLev fan cool?

Well, the magnetic levitation itself is cool:) Also it is more efficient per watt (has more air blow power) than a ball bearing or bushing fan.
In my case the ball bearing fan can blow a lit match from 14 cm away, while the MagLev fan can blow it out from 41 cm(!) away.
So roughly 3 times more blowing power.

What to do if the fan is not able to be driven from PWM output?

Modify it like this:

I discovered my Maglev fans are not able to be driven from PWM output, they only work
with M104 S255, and not any value from 0-254.
Issuing a command less than S255 makes a strange pitch noise instead of turning the fan.

So I started experimenting, and I figured that I only need to add a small capacitor (any electrolite type capacitor works) between 4.7 uF and 100 uF.
(YMMV and also warning: some type of fans does not rotate even with this modification)

Also watch out for the polarity, here there is a pic showing how I modified my two maglev fans:

Aesthetics

I think the capacitor is small enough not to destroy the aesthetic looks of things:

An example of these small fans on the carriage:

(note the superbright yellowish green clamp in the background:)

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I closed down the commenting on this webpage due to the enormous number of penis enlargement suggestions.

If you have any thoughts to share about this article, please discuss it on arcol.hu's mailing list,
in this thread.

Aluminium mounting plate (v4.1.)

I also added an M3 setscrew, to fix the heatsink to the mounting plate
(prevent rotating the whole hotend at high speed).

Also here is how the hotend looks after 6 months of printing:

So the firecement is quite good solution, once it is applied.

Firesleeve added (v4.1.1)

To prevent skin burn, protect heater block against fan blow, and last but not least looks awesome:

Machine compatibility

This hotend is designed for reprap machines (or compatible).
However I had success reports from customers using in 24VDC system, like R2C2 electronics (you need different resistor, so definietly say it before purchase).

I would be really interested how others have mounted or adapted this hotend for their machine,
like makerbot.com or ultimaker.com.

If you happen to have a machine like the above, and you want assistance,
just drop me an email through preorder(at-arcoldothu.

Many people have trouble finding the right spring for the job, so
I decided I will offer the exact same springs, that I use on my own machine.
I settled to this spring after trying out more then 20 different springs.

The ideal spring is small, stiff, but not too hard to compress,
so the hobbed bar (hyena) does not bite into the filament instantly.

Also when you change the filament, the bolt is long enough so you do
not need to take it out completely from the extruder pusher.